1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus having a mechanism for recovering a solvent from a solution containing coloring material that has been ejected onto a recording medium or onto the surface of an intermediate transfer medium.
2. Description of the Related Art
One type of image forming apparatus known in the related art is an inkjet recording apparatus (inkjet printer) having an ink ejection head (inkjet head) in which a plurality of nozzles are arranged. An inkjet recording apparatus of this kind forms an image by ejecting ink from the nozzles in the form of liquid droplets, thereby forming dots on a recording medium, or thereby forming dots on an intermediate transfer body and subsequently transferring it to a recording medium, while the inkjet head and the recording medium or the intermediate transfer body are caused to move relatively with respect to each other.
Various methods are known conventionally as ink ejection methods for an inkjet recording apparatus of this kind. For example, one known method is a piezoelectric method where the volume of a pressure chamber is changed by causing a diaphragm forming a portion of the pressure chamber to deform due to deformation of a piezoelectric element. In this case, ink is introduced into the pressure chamber from an ink supply passage when the volume is increased, and the ink inside the pressure chamber is ejected as a droplet from the nozzle when the volume of the pressure chamber is reduced. Another known method is a thermal inkjet method where ink is heated to generate a bubble in the ink, and ink is then ejected by means of the expansive energy created as the bubble grows.
In an image forming apparatus including an ink ejection head, such as an inkjet recording apparatus, ink is supplied to the ink ejection head from an ink tank which stores ink, via an ink supply channel, and the ink is ejected by one of various methods as described above; however, depending on the type of ink and the type of recording medium or the type of intermediate transfer body, the ink dots (liquid ink droplets) may bleed or blurring of the image may occur due to disruption of the dot shapes after landing of the droplets onto the recording medium, and when a color image is recorded by using inks of a plurality of different colors, bleeding between the different colors and color mixing may occur if ink of one color is recorded in an overlapping fashion onto previously recorded ink of a different color which has not yet dried. This leads to deterioration of image quality.
In order to raise the speed of image recording and improve the quality of the recorded image, it is desirable that the ink solvent should be removed rapidly so that the ink dries quickly. Therefore, in the related art, various technologies have been proposed for removing the ink solvent rapidly so that the ink is caused to dry quickly.
For example, Japanese Patent Application Publication No. 6-47911 discloses a technology in which a recording medium on which a magnetic fluid (liquid) has been deposited is conveyed to a liquid absorbing roller. Upon making contact with the roller, the undried magnetic fluid (liquid) is absorbed by, and confined inside, a temperature-sensitive high-liquid-absorbing resin put onto the periphery of the roller. When recording is not being carried out, the temperature-sensitive high-liquid-absorbing resin is heated to raise the temperature of the resin, whereby the liquid retained inside the resin is discharged and recovered.
Furthermore, for example, Japanese Patent Application Publication No. 2003-182064 discloses a technology in which surplus liquid (solvent) is absorbed by making an auxiliary rotating member (made, for example, of a material such as a sponge roller) provided with a porous, soft and absorbent absorbing layer, or an open cell foam material, come into contact with an intermediate transfer body, whereupon a blade is pressed against the auxiliary rotating member, thereby squeezing out liquid from the auxiliary rotating member. The liquid thus squeezed out is collected in a container and thereby recovered.
Moreover, for example, Japanese Patent Application Publication No. 11-249445 discloses a technology in which a porous roller is placed in contact with a liquid image on a belt, excess liquid is absorbed from the surface of the image via holes and perforations in a skin coating section on the porous main body of the roller, and the liquid is suctioned into a central cavity via the roller skin, by a vacuum source. Moreover, in order to constantly remove the liquid from the developed image on the belt, a vacuum which produces both the negative pressure and positive pressure is generated by a vacuum source and the suctioned excess liquid is expelled to the exterior.
Furthermore, Japanese Patent Application Publication No. 9-15981 discloses an excess developer liquid removal apparatus comprising a liquid absorbing body which removes an excess developing liquid deposited on an image carrier after wet developing of an electrostatic latent image formed on the image carrier. The liquid absorbing body includes at least a surface layer which has air permeability and is made of a material with a surface energy of 25 mJ/m2 or less, and an elastic porous layer formed to the lower layer side of this surface layer. The surface layer forms the outermost layer of the liquid absorbing body that is disposed in the vicinity of, or in contact with, the image carrier.
However, in the technology described in Japanese Patent Application Publication No. 6-47911, it is necessary to recover the liquid absorbed by the temperature-sensitive high-liquid-absorbing resin while the apparatus is not operating, and therefore, if the temperature-sensitive high-liquid absorbing resin has become full with the absorbed liquid during the image recording, then it is necessary to interrupt the image recording in order to recover the absorbed liquid, thus leading to a decline in productivity.
Moreover, in the technology described in Japanese Patent Application Publication No. 2003-182064, a blade-like member is pressed against an auxiliary rotating member made of a material such as a sponge roller, in such a manner that the solvent absorbed by the auxiliary rotating member is expelled and recovered. Since the blade, or the like, applies an external force to a member that is soft, such as a sponge roller, then there is a possibility of deterioration and breakage of the sponge roller and other such members.
Moreover, in the technology described in Japanese Patent Application Publication No. 11-249445, air flows into the porous body in all four directions when the liquid is suctioned from the interior of the porous roller. Therefore, it is difficult to perform suctioning unless the porous body is filled with liquid, and if there is liquid only inside a portion of the porous body, then it is difficult to recover this liquid. Furthermore, in the apparatus disclosed in Japanese Patent Application Publication No. 11-249445, the suctioning force of the porous body is adjusted in order to prevent toner particles from being suctioned into the porous body. If the suctioning force applied to the porous body is too weak, then the absorption speed declines and productivity becomes worse.
Moreover, in the technology described in Japanese Patent Application Publication No. 9-15981, the surface energy is set to be equal to or less than 25 mJ/m2; however, this generally implies a hydrophobic surface and therefore is not suitable for absorbing a solvent whose principal component is water. Furthermore, if the coloring material has aggregated in the solvent, then the coloring material is liable to adhere directly to the surface because the surface is hydrophobic and the coloring material has increased affinity with the hydrophobic surface. Ultimately, it becomes a matter of which material (i.e., the surface where the coloring material is located, or the liquid absorbing body which has a surface energy equal to or less than 25 mJ/m2) has the higher affinity with the coloring material. Therefore, the extent of adherence of the coloring material cannot be determined solely on the basis of the surface energy of the liquid absorbing body alone, and hence it is necessary to establish a relative relationship between the magnitude of the surface energy of the liquid absorbing body and the magnitude of the surface energy of the surface where the coloring material is located.